Polyamide stabilization with copper,mercaptobenzothiazole and halide compounds

ABSTRACT

THE DISCLOSURE OF THIS APPLICATION COMPRISES A PROCESS FOR STABILIZING POLYAMIDES, SUCH AS POLYCAPROLACTAM (NYLON-6) AND POLYHEXAMETHYLENE ADIPAMIDE (NYLON-66) AGAINST THERMAL DECOMPOSITION AND THE THERMALLY STABILIZED COMPOSITIONS PRODUCED THEREBY. THIS STABILIZATION IS EFFECTED BY THE USE OF A THREE-COMPONENT SYSTEM WHICH IS PARTICULARLY ADAPTED TO AVOID THE PLATING OF COPPER ON OTHER METALS WHEN THE STABILIZED COMPOSITION COMES INTO CONTACT WITH SUCH OTHER METALS. THE STABILIZATION OF THIS INVENTION IS EFFECTED BY THE COMBINATION OF 10-60, PREFERABLY 25-50, PARTS PER MILLION OF COPPER IN THE FORM OF A SOLUBLE COPPER COMPOUND, AND 0.05-5, PREFERABLY 0.1-2, PARTS PER HUNDRED OF CERTAIN HALIDE COMPOUNDS, SUCH AS POTASSIUM IODIDE, AND 0.05-5 PARTS, PREFERABLY 0.1-2 PARTS, PER HUNDRED OF MERCAPTOBENZOTHIAZOLE (MBT). THIS COMBINATION HAS A SYNERGISTIC EFFECT IN STABILIZING THE POLYAMIDE EVEN THOUGH THE COPPER COMPOUND IS USED IN SUCH EXTREMELY LOW AMOUNT.

United States Patent 3,558,553 POLYAMIDE STABILIZATION WITH COPPER, MERCAPTOBENZOTPHAZOLE AND HALIDE COMPOUNDS Robert A. Hayes, Cuyahoga Falls, and Joseph H. Tazewell, Akron, Ohio, assignors to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Filed Sept. 3, 1968, Ser. No. 757,128 Int. Cl. C08g N56 US. Cl. 260-4575 10 Claims ABSTRACT OF THE DISCLOSURE The disclosure of this application comprises a process for stabilizing polyamides, such as polycaprolactarn (nylon-6) and polyhexamethylene adipamide (nylon-66) against thermal decomposition and the thermally stabilized compositions produced thereby. This stabilization is effected by the use of a three-component system which is particularly adapted to avoid the plating of copper on other metals when the stabilized composition comes into contact with such other metals. The stabilization of this invention is effected by the combination of 10-60, preferably 25-50, parts per million of copper in the form of a soluble copper compound, and 0.05-5, preferably 0.1-2, parts per hundred of certain halide compounds, such as potassium iodide, and 005-5 parts, preferably 0.1-2 parts, per hundred of mercaptobenzothiazole (MBT). This combination has a synergistic effect in stabilizing the polyamide even though the copper compound is used in such extremely low amount.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to the stabilization of polyamides, such as nylon-6 and nylon-66, against thermal decomposition. More specifically it relates to thermal stabilization of polyamides with a three-component system including copper in such a combination that the copper is not plated onto other metals with which it comes into contact.

Description of the related prior art It is generally known that various copper compounds are effective stabilizers for the oxidative stabilization of polyamides as originally set forth in French Pat. No. 906,893. Among the materials cited in the patent as effective stabilizers are a number of complex double salts including CuCl .KCl.H O. Stamatoif US. Pat. No. 2,705,227 subsequently disclosed the use of copper compounds, alkali metal halides and organophosphites for the stabilization of polyamides.

Zapp US. Pat. No. 3,308,091 discloses that mixtures of cupric acetate, cupric chloride and Z-mercaptobenzothiazole may also be used in the stabilization of polyamides.

However, the proportions of copper shown for practical application are such that copper is plated onto metals that come in contact with the composition. Thus, in the use of polyamides such as nylon-6 and nylon-66 as tire cord, the amount of copper used in such stabilizing compositions as recommended in the above references results in the plating of copper on metals with which the compositions come into contact during processing and utilization.

SUMMARY OF THE INVENTION In accordance with the present invention, it has been found that the thermal degradation or decomposition of polyamides, such as nylon-6 and nylon-66, can be re- 3,558,553 Patented Jan. 26, 1971 tarded or inhibited without the plating out of copper upon contact with another metal, by a three-component stabilizer composition comprising a copper compound, an alkali metal halide, such as KI, :and Z-mercaptobenzothiazole. Moreover it is found that the copper component can be used in such extremely small amounts that there is no plating out of copper when the composition comes in contact with another metal, and that even this small amount of copper has a synergistic effect in the stabilization of polyamide. For the purpose of this invention, the copper is in the proportion of 10-60, preferably 25-50, parts per million, the potassium or other alkali metal halide is present in a proportion of 005-5, preferably 0.1-2, parts per hundred, and the mercaptobenzothiazole in the proportion of 005-5 parts, preferably 0.1-2 parts, per hundred.

The stabilizer composition of this invention is particularly effective in poly-epsilon-caprolactam which is commonly referred to as nylon-6 and which has a plurality of repeating units having the formula (CH CONH-. However the stabilizer composition is also suitable for other linear polyamides made from polymerizable monoamino carboxylic acids or other amide-forming derivatives, or from suitable diamines and dicarboxylic acids or amide-forming derivatives of such compounds. In such other monomeric amines and acids it is desirable to have 3-8 carbon atoms between the amide-forming radicals. Preferred, however, are the nylon-6 described above and nylon-66. The latter is made from adipic acid and hexamethylenediamine. The nylon-66 has the repeating unit structure (CH NHOC(CH CONH.

The polyamides used in the practice of this invention advantageously have an intrinsic viscosity above 0.4 as defined in US. Pat. 2,130,948. Suitable polyamides include: polyhexamethylene adipamide, polyhexamethylene sebacamide, polymerized 6-aminocaproic acid or polyepsilon-caprolactam, polytetramethylene sebacamide, polytetramethylene adipamide and polyadipamides prepared from di(p-aminocyclohexyl)ethane or 1,6-di(paminocyclohexyDhexane as the diamine component. Mixtures of such polyamides can also he used in the practice of this invention.

The copper component can comprise cuprous and cupric salts of an organic or inorganic :acid, and also the copper compounds that are formed when metallic copper or copper oxide is added to the polyamide or to the polyamide forming reactants. In such case compounds are formed which are soluble in the polyamide. Copper salts or aliphatic acids such as acetic, butyric, lauric, palmitic and stearic acids are preferred.

The halide compounds suitable for use in the practice of this invention include the bromides, chlorides and iodides of the alkali metals, such as sodium, potassium and lithium, the alkaline earth metals, including calcium and magnisium, and ammonium bromide, chloride and iodide. Particularly preferred is potassium iodide.

The polyamides can be prepared in the presence of the stabilizer components. Therefore the reagents for preparing the polyamide as well as the components for the stabilizer composition can be intermixed in the original reaction composition. However, the stabilizer compositions of the present invention can be added to the reagents either prior to or during the condensation polymerization, or may be added subsequent to the condensation polymerization. For practical purposes, it is generally preferable to add the stabilizer components to the reagents prior to the condensation polymerization. This insures intimate mixing and avoids an extra subsequent mixing step. However, the stabilizer components may be added to the molten polymer and intimate mixture insured by homogenization, by extrusion or by blending the stabilizer with solid particles of the polyamide in the form 3 of molding powder such as in a tumbler and then extruded for intimate mixing of these solid particles.

In preparing polycaprolactam, it is generally desirable to heat the epsilon-caprolactam at a temperature in the range of 250 to 270 C. in a nitrogen or other inert atmosphere and subsequently to heat the material at a temperature of 250 to 270 C. at a reduced pressure of less than 2 mnr, preferably about 0.5 mm. Hg for a period of at least 6 hours. Polyamides from amino acids can be similarly prepared.

Polyamides such as nylon-66 derived from diamines and diacids are advantageously prepared by heating the corresponding polyamide salt at a temperature of 200- 285 C. in a pressure vessel while releasing gradually the steam generated from the condensation.

The invention is illustrated by the following examples. These examples are intended merely for purpose of illustration and are not intended in any way to limit the scope of the invention nor the manner in Which it may be practiced. Unless specifically provided otherwise, parts and percentages are given by weight.

One of the important properties with respect to polyamide tire cord is the ability to retain tenacity after the tire cord has been exposed to high temperatures for an extended period. This is more or less to determine the ability of the tire cord to retain its tenacity upon being MET KI (p.p.h.) (p.p.h.)

percent retained Cu (p.p.n1.)

tenacity From this table it is seen that the greatest improvement is obtained when both MBT and KI are used with 50 p.p.m. of copper. When these compositions are placed in contact with steel, cast iron, aluminum and other metals there is no plating of copper thereon.

Example II.The procedure of Example I is repeated eight times with the pressure polymerization being conducted for 24 hours at 260 C. under a nitrogen atmosphere, and the subsequent vacuum polymerization being conducted for six hours at 260 C. at 2 mm. Hg. The amounts of reagents and stabilizer components as well as the results are given below in Table II. Again it will be seen that the best results are obtained when the threecomponent stabilizer is used as in Runs 2, 3, 4 and 5.

TABLE II Caproluctam (g.) 300 300 300 300 300 300 300 300 n-Butylamine (ml.) 1. 3S 1. 38 1. 38 1. 38 1. 38 1. 38 1. 38 1. 38 Acetic acid (ml.) 0. 79 0. 79 0. 79 0. 79 0. 79 0.79 0. 034 0. 034 0. 034 0. 034 0. 034 0. 034 3.0 3.0 3.0 3.0 3.0 3.0 25 25 50 25 50 0.3 0.3 0.3 0.3 0.3 KI (g.) 0.3 0.6 0.6 0.3 Initial color Yarn color Percent retained tenacity.. 51. 2 103. 5 115 104. 0 107. 2 09. 8 46. 7 S6. 0

1 Blue. 2 Dark brown. 3 Yellow. 4 Pink-white. 5 Light gray. B Gray. 7 Pink. 9 Off-White.

exposed to high temperatures in both the molding process and in the road conditions under which the tire will be used. The following examples illustrate the effect of the stabilizer compositions on this property.

Example I. Into a beverage bottle in which the atmos- Potassium iodide (KI) 1 Amount indicated in Table I.

The bottle is sealed and shaken to mix the contents before it is placed in a circulating air oven to be heated to 260 C. for 16 hours. At the end of this period the resultant low molecular weight polymer is removed from the bottle and ground in a Wiley mill. The polymer is then remelted in a resin kettle heated by a metal bath. Water and equilibrium lactam are stripped from the molten polymer at 0.2 mm. Hg and 260 C. The resultant polymer is again ground in a Wiley mill and dried under vacuum at 1 mm. Hg overnight at 80 C. The dried polymer is then meltspun into an 18 filament yarn which is subsequently drawn 4.0/1.0 over a hot plate at 310 F. The drawn yarn is aged on a metal rack, at constant length, in a circulating oven at 177 C. for 16 hours. The tenacity after being Example III.T0 a jacketed pressure kettle there is added:

Parts Adipic acid 600 hexamethylcnediamine 600 Distilled water 540 Decolorizing carbon 10 The mixture is stirred for one-half hour and the pH adjusted to 7 by addition of adipic acid or hexamethylenediamine as appropriate. The solution is then filtered and 260 parts (containing sufficient of the salt to make parts of polymer) is concentrated by vacuum distillation. The resulting salt solution is transferred to a glass jar and the stabilizer components added as in Example I. The resulting solution is introduced into a cylindrical glass bottle adapted to fit inside an autoclave having an inside diameter slightly greater than the outside diameter of the bottle and polymerization is carried out by heating over a period of one hour with the temperature gradually increasing from 55 to 215 C. until a pressure of 250 p.s.i. is reached. Steam is gradually bled from the reactor as the temperature is maintained at 215 to 250 C. over a period of 3.75 hours. Then the pressure is gradually released over a period of one hour during which the temperature is maintained at 250-275 C. Then the heating is continued at 275 C. while nitrogen is passed through the autoclave over a period of one hour. The autoclave is then closed and the nitrogen pressure increased to 100 p.s.i. following which the autoclave is cooled and then the plug of polymer in the bottle is recovered after the bottle is broken. The polymer is thev crushed to a powder which is dried in a mechanical convection oven at 120 C. for four hours. The polymer is then melt-spun into yarn as in Example I and after similar processing and testing is found to have similar improved properties as in the yarn of Example I. The procedure is repeated a number of times with the variations in stabilizer components indicated in Table I. Each of the resultant polymers is processed and tested as in Table I with similar improvements noted when the three-component stabilizer system is used as compared to the use of only one or two of the components.

Example IV.The procedures of Examples I and III are repeated using individually in place of the copper acetate an equivalent amount respectively of cuprous chloride, cuprous butyrate, cupric bromide and cuprous laurate. Similar improvements are observed as in Examples I and III when the three-component stabilizer system is used.

Example V.The procedures of Examples I and III are repeated a number of times using individually in place of the potassium iodide an equivalent weight respectively of potassium chloride, sodium bromide, ammonium chloride, calcium chloride and magnesium chloride. Similar improvements are noted as in Examples I and III when the three-component stabilizer system is used.

The polyamides may be described as synthetic linear polycarbonamides having recurring carbonamide groups in the integral part of the main polymer chain. Preferably the carbonamide groups are separated from each other by 3-8 carbon atoms in the form of connecting methylene groups.

The polyamides may be modified by the addition of other materials such as plasticizers, resins, waxes, fillers and various pigments. The particular amide and the use to which it will be put will determine which of such modifying agents are appropriate.

The stabilized polyamides of this invention can be used in any of the forms generally used for polyamides, such as yarns, tire cord, bristles, fabric, molded articles, films and protective coatings such as on filaments, textiles, wood, rubber, leather and ceramic materials.

While certain features of this invention have been described in detail with respect to various embodiments thereof, it will, of course, be apparent that other modifications can be made within the spirit and scope of this invention and it is not intended to limit the invention to the exact details shown above except insofar as they are defined in the following claims.

The invention claimed is:

1. A synthetic linear polycarbonamide having recurring carbonamide groups as an integral part of the main polymer chain which is stabilized against degradative effects of heat and oxygen by the presence of 10-60 parts per million of copper in the form of :a compound soluble in said polycarbonamide, 0.05-5 parts per hundred of 2- mercaptobenzothiazole and 005-5 parts per hundred of a halide selected from the class consisting of alkali metal, alkaline earth metal, hydrogen and ammonium chloride, bromide and iodide, said proportions being based on the weight of said polycarbonamide.

2. The polycarbonamide of claim 1 in which said copper is present in an amount of 25-50 parts per million, said halide is present in an amount of 0.1-2 parts per hundred and said Z-mercaptobenzothiazole is present in an amount of 0.1-2 parts per hundred of said polycarbonamide.

3. A tire cord comprising the polycarbonamide of claim 1.

4. The polycarbonamide of claim 1 in which said polycarbonamide is polyhexamethylene adipamide.

5. The polycarbonamide of claim 4 in which said halid is KI.

6. The polycarbonamide of claim 4 in which said copper is in the form of copper acetate.

7. The polycarbonamide of claim 1 in which said polycarbonamide is poly-epsilon-caprolactam.

8. The polycarbonamide of claim 7 in which said copper is in the form of copper acetate.

9. The polycarbonamide of claim 7 in which said halide is KI.

10. A tire cord comprising the polycarbonamide of claim 9.

References Cited UNITED STATES PATENTS 2,705,227 3/1955 Stamatofi' 260-45.7 3,308,091 3/1967 Zapp 26045.75

DONALD E. CZAJA, Primary Examiner V. P. HOKE, Assistant Examiner US. Cl. X.R.

7322 3? UN 1'. ED STATES PAIIINT 0-1 v CE CERTIFICATE QF CURREC IION Patent NO. Dated 26,

Robert A. Hayes and Joseph H. Tazewell [nventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 57, "Cu(C H 0 .HO" should road Signed and sealed this 23rd day of November 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Acting Commissioner of Patent Attesting Officer 

